compositor-drm: Dont pass ARGB format to addfb2 for primary fbs

compositor-drm: Dont pass ARGB format to addfb2 for primary fbs

Trying to create a ARGB framebuffer for scanout results in EINVAL when
trying to queue the pageflip.  This patch overrides the format we pass
to addfb2 in case of primary buffers like we do for sprites.

Since we always have to inspect and override the format, don't try to
look up the format in drm_fb_get_from_bo().  Instead return format from
drm_output_check_scanout_format().

Rename drm_surface_format_supported() to drm_output_check_sprite_format()
and make it follow the same convention.

We started scanning out ARGB surfaces in commit e920941032979d.